Add chain_getMetadataSeq RPC

core/src/client/client.rs

@@ -505,6 +505,16 @@ impl EngineInfo for Client {
         })
     }
 
+    fn metadata_seq(&self, block_id: BlockId) -> Option<u64> {
+        self.state_info(block_id.into()).map(|state| {
+            state
+                .metadata()
+                .unwrap_or_else(|err| unreachable!("Unexpected failure. Maybe DB was corrupted: {:?}", err))
+                .unwrap()
+                .seq()
+        })
+    }
+
     fn block_reward(&self, block_number: u64) -> u64 {
         self.engine().block_reward(block_number)
     }

core/src/client/mod.rs

@@ -88,6 +88,7 @@ pub trait BlockChainTrait {
 
 pub trait EngineInfo: Send + Sync {
     fn common_params(&self, block_id: BlockId) -> Option<CommonParams>;
+    fn metadata_seq(&self, block_id: BlockId) -> Option<u64>;
     fn block_reward(&self, block_number: u64) -> u64;
     fn mining_reward(&self, block_number: u64) -> Option<u64>;
     fn recommended_confirmation(&self) -> u32;

core/src/client/test_client.rs

@@ -589,6 +589,10 @@ impl EngineInfo for TestBlockChainClient {
         unimplemented!()
     }
 
+    fn metadata_seq(&self, _block_id: BlockId) -> Option<u64> {
+        unimplemented!()
+    }
+
     fn block_reward(&self, _block_number: u64) -> u64 {
         unimplemented!()
     }

rpc/src/v1/impls/chain.rs

@@ -316,6 +316,11 @@ where
         }
     }
 
+    fn get_metadata_seq(&self, block_number: Option<u64>) -> Result<Option<u64>> {
+        let block_id = block_number.map(BlockId::Number).unwrap_or(BlockId::Latest);
+        Ok(self.client.metadata_seq(block_id))
+    }
+
     fn get_possible_authors(&self, block_number: Option<u64>) -> Result<Option<Vec<PlatformAddress>>> {
         Ok(self.client.possible_authors(block_number).map_err(errors::core)?)
     }

rpc/src/v1/traits/chain.rs

@@ -145,6 +145,10 @@ build_rpc_trait! {
         #[rpc(name = "chain_getTermMetadata")]
         fn get_term_metadata(&self, Option<u64>) -> Result<Option<(u64, u64)>>;
 
+        /// Return the current metadata seq at given block number
+        #[rpc(name = "chain_getMetadataSeq")]
+        fn get_metadata_seq(&self, Option<u64>) -> Result<Option<u64>>;
+
         /// Return the valid block authors
         #[rpc(name = "chain_getPossibleAuthors")]
         fn get_possible_authors(&self, Option<u64>) -> Result<Option<Vec<PlatformAddress>>>;